1. Field of the Invention
The present invention relates to devices for the maintenance of large-capacity containers, such as storage tanks or the like vessels, having preferably an at least approximately round cross section.
2. Prior Art
Large-capacity containers of the here pertinent variety are tanks used for the storage of gases or liquids of any nature, such as city gas, petroleum, various petroleum fractions and other fluids, but also of solids such as fine dusts or the like. Such storage tanks are usually structures which are symmetrical with respect to rotation seen from a central, vertical axis, and are generally of cylindrical, or spherical form. Since their height often corresponds to that of a building of several stories and they are frequently accessible only with difficulties on account of their specific locations, their maintenance results to be difficult, time-consuming and therefore expensive in a large number of practical cases.
The maintenance of storage tanks is, however, of prime importance, particularly if they contain easily inflammable, chemically aggressive or even explosive substances, such maintenance being therefore logically required in relatively short intervals by law, even though such laws and regulations may differ in wording, according to the countries concerned.
The scaffolding of such large-capacity containers using commercial structures, such as scaffolding tubes with clamp straps, and the provision of a plurality of working platforms which are superposed one above the other with the scaffolding structure and are accessible by means of ladders, is known.
The existing tank containers having a circular cross section are usually scaffolded by segments, i.e., by only certain partial areas of their peripheral area, so as to successively carry out the required maintenance work on such large-capacity containers; such as renewing or repair work of any nature gradually by continued rescaffolding parts of such containers. The parts of the scaffold must therefore not be tied to the container walls in a form that the walls would be damaged due to drilling or the application of fitting plates or be exposed to other additional loads. The above mentioned scaffold structures therefore require additional stabilizing jacks and/or supporting struts placed outside of the scaffold structure, hampered often by difficult subsoil conditions such as loose sands or ditches around such large-capacity containers.
Aside from such total scaffoldings or segment-wise scaffolding with its successive time-consuming scaffold constructions, also a variety of suspended platforms have been known, such platforms using a method in which a working platform is practically suspended on two ropes which are fastened to the upper edge of such container at a certain spot and are movable along its total height by way of a lift. This is done by means of a crank handle provided on the working platform or also by an electric motor which raises the working platform or optionally lowers it. Repair work is possible in such cases only along the small segment section of the large-capacity container as determined by the length of the suspended working platform. Also in such cases, both the remounting of the suspended platform and new securing from section to section are required.
In addition to the difficulties of the known scaffold structures for the maintenance of large-capacity containers, it must be taken into consideration that such storage tanks may be provided with solid roof structures or with floating roofs, in accordance with their purpose, and also with covers of different shapes, e.g., also with such containers having central air shafts or so-called dome superstructures, or that they may be flat-floor tanks with double walls.